Holographic storage layer, holographic disk using the same, and method for manufacturing the same

ABSTRACT

A holographic storage layer includes a reflective structure and photosensitive units. The reflective structure is a grid-shaped structure and includes cavities. The photosensitive units are disposed in the cavities, in which each of the photosensitive units is surrounded by the reflective structure. First openings and second openings are defined by the reflective structure, and the photosensitive units are exposed by the first openings and the second openings respectively.

RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.14/660,921, filed Mar. 17, 2015, which claims priority from TaiwaneseApplication Serial Number 103145619, filed Dec. 26, 2014. All of theseapplications are incorporated herein by reference.

BACKGROUND

Technical Field

The present disclosure relates to a holographic storage layer, aholographic disk using the same, and a method for manufacturing thesame.

Description of Related Art

With the development of technology, the amount of storage capacityrequired for electronic files has correspondingly increased. A typicalway of storing data involves recording magnetic or optical changes onthe surface of a recording medium, and the magnetic or optical changesare taken as the basis of the data. Examples of such recording mediumsinclude floppy disks and compact discs. However, with continuedincreases in the amount of storage capacity required for electronicfiles, the development of holographic storage technology has beenattracting the attention of those in the field.

With holographic storage technology, image data can be written into arecording medium (a photosensitive medium) via interference between asignal light beam and a reference light beam. When reading the imagedata, the image data can be generated by emitting the reference lightbeam into the recording medium (photosensitive medium) again. Next, theimage data is generated, and the generated mage data can be read by adetector. In other words, the storage capacity of holographic storagetechnology is related to the recording medium (photosensitive medium).

SUMMARY

An aspect of the present invention provides a holographic storage layerincluding a reflective structure, in which the reflective structureincludes cavities for confining a diffusion area of a writing lightbean. Therefore, when data is, written into the holographic storagelayer, the writing light beam formed by a reference light beam and asignal light beam is confined in a region defined by the cavities, suchthat the degree of mixing between the reference light beam and thesignal light beam is enhanced. That is, a usage rate of photosensitivematerial in the cavities is increased.

An aspect of the present invention provides a holographic storage layerincluding a reflective structure and photosensitive units. Thereflective structure is a grid-shaped structure and includes cavities.The photosensitive units are disposed in the cavities, in which each ofthe photosensitive units is surrounded by the reflective structure.First openings and second openings are defined by the reflectivestructure, and the photosensitive units are exposed by the firstopenings and the second openings respectively.

In some embodiments, an area of each of the first openings and thesecond openings is in a range from 0.1 μm² to 24 mm².

In some embodiments, the reflective structure is circular, and anarrangement of the cavities is symmetrical about a circle center of thereflective structure.

In some embodiments, the cavities are sector-shaped, in which each ofthe cavities includes two curved boundaries, and the curved boundariesand the reflective structure have the same circle center.

In some embodiments, an area of the photosensitive units exposed by thefirst openings or the second openings occupies a range from 50% to 99.9%of a total area of the holographic storage layer.

In some embodiments, at least one sidewall of each of the cavities and anormal direction of the holographic storage layer intersect at an angle.

In some embodiments, the angle is in a range from −45 degrees to 45degrees.

In some embodiments, a first group of the photosensitive units isgradually widened from the corresponding first openings to thecorresponding second openings, and a second group of the photosensitiveunits is gradually narrowed from the corresponding first openings to thecorresponding second openings.

In some embodiments, the holographic storage layer further includeslight-absorbing units disposed on a surface of the reflective structure,in which the light-absorbing units are located adjacent to the firstopenings and the second openings.

In some embodiments, the holographic storage layer further includesreflective units, in which the reflective units are disposed on thefirst openings corresponding to a first group of the photosensitiveunits and the second openings corresponding to a second group of thephotosensitive units.

In some embodiments, the first group of the photosensitive units and thesecond group of the photosensitive units are arranged alternately.

In some embodiments, a shape of each of the cavities projected to asurface of the holographic storage layer is circular, rectangular,triangular, or polygonal.

In some embodiments, the holographic storage layer further includessidewalls and at least one adhesive unit. The cavities are defined bythe sidewalls. The adhesive unit is disposed between the sidewalls forfixing the sidewalls.

An aspect of the present invention provides a holographic disk includinga first substrate, a second substrate, and a holographic storage layer.The holographic storage layer is, disposed between the first substrateand the second substrate and includes a reflective structure andphotosensitive units. The reflective structure is a grid-shapedstructure and includes cavities. The photosensitive units are disposedin the cavities, in which each of the photosensitive units is surroundedby the reflective structure. A plurality of first openings and secondopenings are defined by the reflective structure, and the photosensitiveunits are exposed by the first openings and the second openingsrespectively.

In some embodiments, the first substrate and the second substrate aretransparent substrates.

In some embodiments, the first substrate is transparent substrate andthe second substrate is a reflective substrate.

An aspect of the present invention provides a method for manufacturing aholographic storage layer. The method includes a number of steps.Reflective layers are respectively formed on strip-shaped photosensitivesubstances. The photosensitive substances are arranged in a parallelarrangement for making the photosensitive substances into a bundle-shapeconfiguration, in which a space between the reflective layers is filledwith at least one adhesive unit to realize the bundle shape of thephotosensitive substances. The photosensitive substances are cut, inwhich a cutting direction and a lengthwise direction of thephotosensitive substances provided in the bundle-shape configuration areorthogonal.

An aspect of the present invention provides a method for manufacturing aholographic storage layer. The method includes a number of steps. A moldis filled with a reflective material and a reflective structure isformed by casting the reflective material in which the reflectivestructure includes cavities. The cavities are filled with aphotosensitive material, and then the photosensitive material issolidified.

In some embodiments, the method further includes planarizing the solidphotosensitive material and the reflective structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a holographic disk accordingto the first embodiment of this invention;

FIG. 2 is an enlarged view of area A in FIG. 1;

FIG. 3 is a side view of a holographic disk according to the secondembodiment of this invention;

FIG. 4A is a top view of a holographic disk according to the thirdembodiment of this invention;

FIG. 4B is an enlarged view of a cavity in a reflective structure inFIG. 4A;

FIG. 5A is a perspective view of a holographic disk according to thefourth embodiment of this invention;

FIG. 5B is a side view of cavities arranged along a radial direction ofa holographic disk according to the fourth embodiment of this invention;

FIG. 5C is a side view of cavities arranged along a tangent direction ofa holographic disk according to the fourth embodiment of this invention;

FIG. 6A to FIG. 6D are top views of a reflective structure of aholographic disk according to various embodiments of this invention;

FIG. 7A to FIG. 7D are perspective views of a method for manufacturing aholographic storage layer according to an embodiment of this invention;and

FIG. 8A to FIG. 8G are side views of a method for manufacturing aholographic storage layer according to another embodiment of thisinvention.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the disclosed embodiments. It will be apparent,however, that one or more embodiments may be practiced without thesespecific details. In other instances, well-known structures and devicesare schematically shown in order to simplify the drawing.

In a holographic storage system, when data is written into a holographicdisk, a writing light beam formed by a signal light beam and a referencelight beam is required to perform exposure and interference in a certainarea of a photosensitive unit. However, in the photosensitive unit,since the actual area used for storing data is smaller than the exposedarea, parts of the photosensitive unit are not utilized, and hence ausage rate of the photosensitive unit is decreased. Moreover, when theusage rate of the photosensitive material is decreased, the storagecapacity of the holographic disk is reduced.

In view of this, a holographic storage layer of the present inventionincludes a reflective structure, in which the reflective structureincludes cavities, for confining a diffusion area of a writing lightbeam. With the cavities of the reflective structure, when a light beamenters the holographic storage layer, the light beam is confined in aspecific area, such that interference and exposure occur in thisspecific area. Therefore, the extent of mixing between a reference lightbeam and the signal light beam is enhanced, and the usage rate of thephotosensitive material is increased. Moreover, since the usage rate ofthe photosensitive material is increased, the storage capacity of theholographic disk is also improved.

FIG. 1 is an exploded perspective view of a holographic disk accordingto the first embodiment of this invention. FIG. 2 is an enlarged view ofarea A in FIG. 1.

A holographic disk 100 includes a first substrate 102, a secondsubstrate 104, and a holographic storage layer 110. The holographicstorage layer 110 is disposed between the first substrate 102 and thesecond substrate 104 and includes a reflective structure 120 andphotosensitive units 132. The reflective structure 120 is a grid-shapedstructure and includes cavities 130. The photosensitive units 132 aredisposed in the cavities 130, in which each of the photosensitive units132 is surrounded by the reflective structure 120. First openings 122and second openings 124 are defined by the reflective structure 120, andthe photosensitive units 132 are exposed by the first openings 122 andthe second openings 124 respectively.

As shown in FIG. 2, the reflective structure 120 includes sidewalls 134to define each of the cavities 130, and the photosensitive units 132located in the cavities 130 are separated from each other by thesidewalls 134. The photosensitive units 132 are made of an opticalstorage material or a photosensitive material. With this configuration,when a writing light beam formed by a signal light beam S and areference light beam R enters one of the cavities 130, the writing lightbeam is reflected at the sidewalls 134 of the cavity 130. In otherwords, each of the cavities 130 is used for confining a diffusion areaof the writing light beam, and the writing light beam is limited to thesingle cavity 130.

For example, when the holographic disk 100 is in a writing operation (ora reading operation), the writing light beam formed by the signal lightbeam S and the reference light beam R enters the cavities 130, and thephotosensitive units 132 are interfered by the writing light beam. Sincethe writing light beam is limited to one of the cavities 130, the extentof mixing between the signal light beam S and the reference light beam Ris enhanced. Therefore, the usage rate of the photosensitive unit 132 isincreased, and the storage capacity of the holographic disk 100 isimproved.

In some embodiments, the first substrate 102 is a transparent substrateand the second substrate 104 is a reflective substrate. Therefore, thewriting light beam enters the holographic storage layer 110 through thefirst openings 122 facing the first substrate 102. As far as the signallight beam S and the reference light beam R entering the cavities 130via the first openings 122 are concerned, when the signal light beam Sand the reference light beam R leave the holographic storage layer 110from the second openings 124, the signal light beam S and the referencelight beam R are reflected from the second substrate 104 and returned tothe holographic storage layer 110.

In addition, when the writing light beam enters the holographic storagelayer 110 from a side of the first substrate 102, the first openings 122are regarded as light entrances of the cavities 130 for the writinglight beam, in which an area of each of the light entrances correspondsto a required minimum nyquist aperture of the writing light beam.

As far as the area of interference between the signal light beam S andthe reference light beam R is concerned, the narrowest width of adistribution of the signal light beam S and the reference light beam Rin the cavity 130 is in the range between one and two times the width ofthe minimum nyquist aperture. Therefore, the area of each of the firstopenings 122 regarded as the light entrance is greater than the area ofthe narrowest region of the cavities 130 interfered by the signal lightbeam S and the reference light beam R, such that the signal light beam Sand the reference light beam R are not affected by the scale of thecavities 130 and can complete the writing operation. Limitations withrespect to the nyquist aperture are described further below.

The nyquist aperture is determined by the following equation I:D _(v)=(fλ)/δv  Equation I

-   -   where D_(v) is the width of the aperture in the v direction, f        is the focus of the focusing lens, λ is the wavelength of the        optical wave in the medium, and δv is the minimum resolution of        the signal in the v direction.

For example, assuming the holographic disk 100 is written by a spatiallight modulator (SLM) with a 3.5 μm×3.5 μm pixel unit, and a light beamemitted by the SLM is passed through a relay lens, after the light beamis reduced by 3.5 times by the relay lens, an input signal with a 1 μm×1μm resolution is generated on a front focal plane of an object lens, inwhich the focus of the object lens is 4 mm, and the wavelength of thelight beam in the medium is 0.4 μm. According to equation I, in orderfor a light beam to be able to pass through the cavities 130, a focalplane of the object lens must have a 1.6 mm×1.6 mm aperture. In otherwords, under such conditions, the area of the light entrance of each ofthe cavities 130 is at least equal to or greater than 2.56 mm².

Moreover, as another example, assuming the light beam emitted by theobject lens is a plane wave without modulation, the narrowest region ofthe light distribution is a light point with a diffraction limit, andthus D_(v) is 0.61λ. Under such conditions, if the wavelength of thewriting light beam is 0.4 μm, the area of the light entrance of each ofthe cavities 130 is at least equal to or greater than 0.244 μm².

Furthermore, the minimum area of the light entrance of each of thecavities 130 has to be such that all image data can be restructured. Forexample, even though the nyquist aperture is designed to allow the imagedata (the writing light beam) to pass therethough, in which the minimumarea of the light entrance of each of the cavities 130 is between oneand two times nyquist aperture in theory, the apertures of the cavities130 can be further reduced by applying the run-length-limited code (RLLcode). On the other hand, in the case where the input signal istwo-level intensity or phase encoding, a distribution of the light fieldon the focal plane of the object lens is axially symmetric, and hencethe apertures of the cavities 130 can be further reduced.

As previously described, the area of the light entrances of the cavities130 corresponds with the need for the minimum nyquist aperture of thewriting light beam. In different writing conditions (or different waysof writing), the light entrances of the cavities 130 may have differentareas. Therefore, in order to correspond with such different ways ofwriting, in some embodiments, an area of each of the first openings 122and the second openings 124 is in the range from 0.1 μm² to 24 mm².

Furthermore, since a percentage that the photosensitive units 132occupying in the holographic storage layer 110 is highly related to thestorage capacity of the holographic storage layer 110, in someembodiments, an area of the photosensitive units 132 exposed by thefirst openings 122 or the second openings 124 occupies a range from 50%to 99.9% of a total area of the holographic storage layer 110. Here, ifthe area of the photosensitive units 132 occupies less than 50% of thetotal area of the holographic storage layer 110, the holographic storagelayer 110 may have a low storage capacity. If, on the other hand, thearea of the photosensitive units 132 occupies more than 99.9% of thetotal area of the holographic storage layer 110, a complex manufacturingprocess may be needed and the yield rate of the holographic storagelayer 110 is decreased.

In some embodiments, the holographic storage layer 110 further includeslight-absorbing units 160. The light-absorbing units 160 are disposed ona surface of the reflective structure 120, in which the light-absorbingunits 160 are located at regions adjacent to the first openings 122 andthe second openings 124. In other words, the surface of the reflectivestructure 120 corresponding to the sidewalls 134 is covered with thelight-absorbing units 160. Therefore, when the writing light beam isemitted toward the holographic storage layer 110, if the writing lightbeam does not enter the first openings 122 or the second openings 124,the writing light beam is absorbed by the light-absorbing units 160.Furthermore, the reflective structure 120 can be filled with thelight-absorbing units 160 during the manufacturing process of thereflective structure 120. Moreover, the light-absorbing units 160 alsocan be coated on the reflective structure 120 before the reflectivestructure 120 is filled with the photosensitive units 132. Thereforeafter disposing the photosensitive units 132 the photosensitive units132 and the light-absorbing units 160 are coplanar.

In other words, when the signal light beam S and the reference lightbeam R are emitted at a region out of the first openings 122 or thesecond openings 124, the signal light beam S and the reference lightbeam R are absorbed by the light-absorbing units 160, such that noise isreduced during the writing operation of the holographic storage layer110. For example, as shown in FIG. 2, when the signal light beam S andthe reference light beam R are emitted onto the surface of theholographic storage layer 110 corresponding to the sidewalls 134, thesignal light beam S and the reference light beam R are absorbed by thelight-absorbing units 160 so as to prevent the signal light beam S andthe reference light beam R from being reflected from the surface of thesidewalls 134.

FIG. 3 is a side view of a holographic disk according to the secondembodiment of this invention. As shown in FIG. 1 and FIG. 3, thedifference between this embodiment and the first embodiment is that theholographic storage layer 110 of the holographic disk 100 furtherincludes reflective units 170. The reflective units 170 are disposed ona portion of the first openings 122 and the second openings 124, suchthat each of the cavities 130 corresponding to the writing light beamhas only one light entrance.

In some embodiments, the first substrate 102 and the second substrate104 are transparent substrates. Therefore, the writing light beam canenter the holographic storage layer 110 not only via the first openings122 facing the first substrate 102, but also via the second openings 124facing the second substrate 104.

In the present embodiment, the photosensitive units 132 are divided intotwo groups, in which the photosensitive units 132 a belong to a firstgroup and the photosensitive units 132 b belong to a second group. Thereflective units 170 are disposed on the first openings 122corresponding to the first group of the photosensitive units 132 (thephotosensitive units 132 a) and the second openings 124 corresponding tothe second group of the photosensitive units 132 (the photosensitiveunits 132 b). By disposing the reflective units 170 in this manner, thewriting light beams propagated from the first substrate 102 and thesecond substrate 104 are respectively reflected at the positionscorresponding to the photosensitive units 132 a and the photosensitiveunits 132 b. Therefore, the photosensitive units 132 a receive thewriting light beam propagated from the second substrate 104 via thesecond openings 124, and the photosensitive units 132 b receive thewriting light beam propagated from the first substrate 102 via the firstopenings 122.

Furthermore, the reflective units 170 can be formed simultaneouslyduring the manufacture process of the reflective structure 170, suchthat the reflective units 170 and the photosensitive units 132 exposedby the first openings 122 or the second openings 124 are coplanar.Alternatively, the reflective units 170 also can be formed afterdisposing the photosensitive units 132, and the photosensitive units 132and the reflective units 170 formed on the photosensitive units 132 areplanarized together such that the reflective units 170 and thephotosensitive units 132 are coplanar.

In this configuration, the writing light beam formed by the signal lightbeam S and the reference light beam R can be emitted toward theholographic disk 100 from the top and bottom sides of the holographicdisk 100 simultaneously. In greater detail, the first group of thephotosensitive units 132 (the photosensitive units 132 a) receiving thewriting light beam via the second openings 124 and the second group ofthe photosensitive units 132 (the photosensitive units 132 b) receivingthe writing light beam via the first openings 122 are arrangedalternately.

FIG. 4A is a top view of a holographic disk according to the thirdembodiment of this invention. FIG. 4B is an enlarged view of a cavity inthe reflective structure in FIG. 4A. The difference between thisembodiment and the first embodiment is that the holographic storagelayer 110 and the reflective structure 120 of the present embodiment arecircular, and the cavities 130 in the reflective structure 120 arearranged following along an orbital path.

In the present embodiment, the holographic storage layer 110 and thereflective structure 120 are circular, and the arrangement of thecavities 130 is symmetrical about a circle center of the reflectivestructure 120. In other words, the cavities 130 of the reflectivestructure 120 are arranged following along an orbital path about ashared circle center of the holographic storage layer 110 and thereflective structure 120. Moreover, the cavities 130 are sector-shaped,in which each of the cavities 130 includes two curved boundaries.Similarly, the curved boundaries, the holographic storage layer 110, andthe reflective structure 120 have the same circle center. That is, eachof the cavities 130 includes two curved sidewalls 134, in which the twosidewalls 134 and the reflective structure 120 have the same circlecenter.

In this configuration, the cavities 130 of the reflective structure 120are arranged with a higher density. Additionally, since thephotosensitive units 132 are disposed in the cavities 130, thepercentage of the photosensitive units 132 occupying in the holographicstorage layer 110 is increased by this arrangement. Therefore, thestorage capacity of the holographic storage layer 110 is improved. Inthe following description, arrangements are described that increase thedensity of the cavities 130 in the holographic storage layer 110.

FIG. 5A is a perspective view of a holographic disk according to thefourth embodiment of this invention. As shown in FIG. 5A, the differencebetween this embodiment and the third embodiment is that the firstopening 122 and the second opening 124 corresponding to the same cavity130 have different areas.

As previously described, the cavities 130 are sector-shaped when viewedfrom above. In order to arrange the cavities 130 with a higher density,the first opening 122 and the second opening 124 corresponding to thesame cavity 130 have different areas, such that the cavities 130 and thephotosensitive units 132 disposed in the cavities 130 are graduallywidened or narrowed from the corresponding first openings 122 to thecorresponding second openings 124. Furthermore, in this configuration,with respect to the two sidewalls 134 (see FIG. 4B) defining thecavities 130, an angle between these two sidewalls 134 and the surfaceof the holographic storage layer 110 (see FIG. 4A) is a non-right angle.

FIG. 5B is a side view of cavities arranged along a radial direction ofa holographic disk according to the fourth embodiment of this invention.As shown in FIG. 5A and FIG. 5B, the cavities 130 of FIG. 5A and FIG. 5Bhave the same shape. To facilitate the description to follow, FIG. 5Aand FIG. 5B are illustrated in the same cylindrical coordinate systemwith a radial direction X, a tangent direction Y, and an axial directionZ. Furthermore, and again to facilitate the description to follow, amongthe four sidewalls 134 corresponding to each of the cavities 130, twocurved sidewalls 134 are marked as sidewalls 134 a, and other twosidewalls 134 are marked as sidewalls 134 b.

In some embodiments, at least one sidewall 134 of each of the cavities130 and a normal direction 150 of the holographic storage layer 110intersect at an angle θ, in which the angle θ is in the range from −45degrees to 45 degrees. That is, the two sidewalls 134 a of each of thesector-shaped cavities 130 are slanted to the surface of the holographicstorage layer 110, in which these two sidewalls 134 a are disposed alongthe radial direction X of the holographic storage layer 110. The othertwo sidewalls 134 b of each of the sector-shaped cavities 130 and thesurface of the holographic storage layer 110 are perpendicular, in whichthese two sidewalls 134 b are disposed along the tangent direction Y ofthe holographic storage layer 110.

In this configuration, the photosensitive units 132 can be divided intotwo portions, in which the photosensitive units 132 a belong to a firstportion and the photosensitive units 132 b belong to a second portion.The first portion of the photosensitive units 132 (the photosensitiveunits 132 a) is gradually widened from the corresponding first openings122 to the corresponding second openings 124, and the second portion ofthe photosensitive units 132 (the photosensitive units 132 b) isgradually narrowed from the corresponding first openings 122 to thecorresponding second openings 124.

Furthermore, the holographic storage layer 110 of the present embodimentfurther includes the reflective units 170, and the reflective units 170are disposed at some of the first openings 122 and the second openings124. The reflective units 170 of the present embodiment are similar tothe reflective units 170 of the second embodiment. That is, thereflective units 170 are disposed at the first openings 122corresponding to the photosensitive units 132 a and the second openings124 corresponding to the photosensitive units 132 b. In other words, theholographic storage layer 110 of the present embodiment can receive thewriting light beam from the top and bottom sides of the holographicstorage layer 110 during the writing operation. Moreover, since thesidewalls 134 a and the normal direction 150 of the holographic storagelayer 110 intersect at the angle θ, the probability that the signallight beam S and the reference light beam R (see FIG. 2) are reflectedat the sidewalls 134 a is increased. Therefore, the extent of mixingbetween the signal light beam S and the reference light beam R isenhanced, and the storage capacity of the holographic storage layer 110is improved.

FIG. 5C is a side view of cavities arranged along a tangent direction ofa holographic disk according to the fourth embodiment of this invention.As shown in FIG. 5A and FIG. 5C, the cavities 130 of FIG. 5A and FIG. 5Chave the same shape. To facilitate the description to follow, FIG. 5Aand FIG. 5C are illustrated in the same cylindrical coordinate systemwith the radial direction X, the tangent direction Y, and the axialdirection Z. Furthermore, the cavities 130 in FIG. 5C are arranged alongthe tangent direction Y.

As previously described, the two sidewalls 134 b opposite the curvedboundaries of the cavities 130 and the holographic storage layer 110 areperpendicular. Therefore, in the tangent direction Y, each of thesidewalls 134 b between the cavities 130 and the surface of theholographic storage layer 110 are perpendicular, and the sidewalls 134 band the direction Z are parallel.

As a result, the cavities 130 of the reflective structure 120 of thepresent embodiment are arranged in a closely packed configuration, andthe holographic storage layer 110 can receive the writing light beam(which includes the signal light beam and the reference light beam)propagated from the top and bottom sides of the holographic storagelayer 110 under this arrangement. Furthermore, in the presentembodiment, the two sidewalls 134 a of the cavities 130 arranged alongthe radial direction X are slanted to the surface of the holographicstorage layer 110, and the two sidewalls 134 b of the cavities 130arranged along the tangent direction Y and the surface of theholographic storage layer 110 are perpendicular. However, a personhaving ordinary skill in the art may choose a proper arrangement of thesidewalls 134. For example, the two sidewalls 134 a of the cavities 130with the curved boundaries and the surface of the holographic storagelayer 110 may be perpendicular, and the other sidewalls 134 b oppositethe two sidewalls 134 a may be slanted to the surface of the holographicstorage layer 110.

FIG. 6A to FIG. 6D are top views of a reflective structure of aholographic disk according to various embodiments of this invention. Insome embodiments, a shape of each of the cavities 130 of the reflectivestructure 120 projected to the surface of the holographic storage layer110 and the reflective structure 120 is circular, triangular,rectangular, or polygonal (respectively illustrated in FIG. 6A, FIG. 6B,FIG. 6C, and FIG. 6D). Similarly, the cavities 130 are arranged in aclosely packed configuration. Therefore, the usage rate of thephotosensitive units 132 is increased, and the storage capacity of theholographic storage layer 110 is improved.

Furthermore, in some embodiments, the reflective frame structure 120further includes sidewalls 134 and at least one adhesion unit 180. Thecavities 130 are defined by the sidewalls 134. The adhesion unit 180 isdisposed between the sidewalls 134 for fixing and connecting thesidewalls 134. As shown in FIG. 6A, each of the circular cavities 130has the corresponding sidewall 134, and the adhesive unit 180 isdisposed in a space between the sidewalls 134. After the sidewalls 134are fixed, the reflective structure 120 formed by the sidewalls 134 isobtained. However, a person having ordinary skill in the art may choosea proper manner in which to form the reflective structure 120. Forexample, the sidewalls 134 of the reflective structure 120 may be formedin one piece.

FIG. 7A to FIG. 7D are perspective views of a method for manufacturing aholographic storage layer according to an embodiment of this invention.The method for manufacturing a holographic storage layer according tothis embodiment includes a number of steps. First, reflective layers 190are formed, in which the reflective layers 190 are formed respectivelyon the surfaces of strip-shaped photosensitive substances 192. Next, thephotosensitive substances 192 are arranged in a parallel arrangement sothat the photosensitive substances 192 are provided in a bundle-shapeconfiguration, and a space between the reflective layers 190 is filledwith at least one adhesion unit 180 to realize the bundle shape of thephotosensitive substances 192. Subsequently, the photosensitivesubstances 192 are cut, in which a cutting direction and a lengthwisedirection of the photosensitive substances 192 provided in thebundle-shape configuration are orthogonal. The above steps will bedescribed in greater detail below.

As shown in FIG. 7A, the photosensitive substance 192 is a bar made ofan optical storage material or a photosensitive material. The reflectivelayers 190 are formed on the surfaces of the strip-shaped photosensitivesubstance 192, in which the reflective layers 192 can be formed bycoating or vapor depositing reflective material.

As shown in FIG. 7B, the photosensitive substances 192 covered with thereflective layers 190 are arranged in a bundle-shape configuration or anarray. Next, a space between the photosensitive substances 192 coveredwith the reflective layers 190 is filled with at least one adhesion unit180, such that the photosensitive substances 192 covered with thereflective layers 190 are formed into the bundle-shape configuration.

As shown in FIG. 7C, the photosensitive substances 192 formed into thebundle-shape configuration are cut, in which the cutting direction andthe lengthwise direction of the photosensitive substances 192 providedin a bundle-shape configuration are orthogonal. That is, thephotosensitive substances 192 are cut in a transverse direction. Aftercutting the photosensitive substances 192, the photosensitive substances192 covered with the reflective layers 190 are formed into a sheetstructure, as shown in FIG. 7D. Moreover, after burnishing this sheetstructure, the reflective structure of the holographic storage layer inFIG. 1 is obtained.

FIG. 8A to FIG. 8G are side views of a method for manufacturing aholographic storage layer according to another embodiment of thisinvention. The method for manufacturing a holographic storage layeraccording to this embodiment includes a number of steps. A mold 196 isfilled with a reflective material 194 and a reflective structure 120 isformed by casting the reflective material 194, in which the reflectivestructure 120 includes cavities 130. The cavities 130 are filled withphotosensitive materials 200, and then the photosensitive materials 200are solidified. Details of the above steps will now be described.

As shown in FIG. 8A, the mold 196 is filled with the reflective material194, in which the mold 196 includes trenches 198. In addition, beforethe trenches 198 of the mold 196 are filled with the reflective material194, the reflective material 194 can be heated in preparation for thecasting process.

As shown in FIG. 8B, after the trenches 198 of the mold 196 are filledwith the reflective material 194, the reflective material 194 permeatesinto the trenches 198. In order to improve the yield rate of thereflective material 194, this casting step can be performed under atleast a low vacuum state, such that the air remaining in the mold 196 isreduced.

As shown in FIG. 8C, the reflective material 194 undergoes a demoldingprocess, such that the reflective material 194 is separated from themold 196 to form a reflective structure 120. Similarly, in order toimprove the yield rate of the reflective material 194, this demoldingprocess can be performed under a high vacuum state, such that anair-pressure difference between the air in the mold 196 and the externalair is formed. The reflective material 194 can be easily taken out as aresult of this air-pressure difference. Furthermore, the reflectivestructure 120 formed from the reflective material 194 includes thecavities 130 corresponding to the trenches 198.

As shown in FIG. 8D and FIG. 8E, the cavities 130 of the reflectivestructure 120 are filled with the photosensitive materials 200, and thephotosensitive materials 200 are solidified to form photosensitive units132. In order to improve the yield rate of the photosensitive units 132,this step can be performed under a high vacuum state, such that the airremaining in the cavities 130 of the reflective structure 120 isreduced.

Furthermore, in some embodiments, the method further includesplanarizing the solid photosensitive materials 200 and the reflectivestructure 120. In this case, if the vacuum state in the solidifying stepis weak, the photosensitive materials 200 will be deformed due toundergoing shrinkage, and the surface of the photosensitive units 132will not be level, as shown in FIG. 8F.

As shown in FIG. 8G, the photosensitive units 132 with the unlevelsurface and the reflective structure 120 are planarized, in which theplanarizing step includes burnishing or polishing the surfaces of thephotosensitive units 132 and the reflective structure 120 by a burnisher202.

By the above steps, the reflective structure 120 and the photosensitiveunits 132 located in the cavities 130 of the reflective structure 120are formed, in which a combination of the reflective structure 120 andthe photosensitive units 132 is similar to the holographic storage layerin FIG. 1.

As a result, the holographic storage layer of the present inventionincludes the reflective structure, in which the reflective structureincludes cavities for confining the diffusion area of the writing lightbeam. When the holographic storage layer is in the writing operation,the interference and exposure occurring by the application of a writinglight beam is confined in this area, such that the extent of mixingbetween a reference light beam and the signal light beam is enhanced.Therefore, with the cavities for confining the diffusion area of thewriting light beam, the usage rate of the photosensitive material isincreased, and the storage capacity of the holographic disk is alsoimproved.

Although the present invention has been described in considerable detailwith reference to certain embodiments thereof, other embodiments arepossible. Therefore, the spirit and scope of the appended claims shouldnot be limited to the description of the embodiments contained herein.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims.

What is claimed is:
 1. A method for manufacturing a holographic storagelayer, comprising: forming a plurality of reflective layers on aplurality of strip-shaped photosensitive substances respectively;arranging the photosensitive substances in a parallel arrangement;filling a space between the reflective layers with an adhesive such thatthe reflective layers are adhered by the adhesive therebetween; andcutting the photosensitive substances, wherein the cutting thephotosensitive substances is performed after filling the space with theadhesive, and a cutting direction and a lengthwise direction of thephotosensitive substances provided in the bundle-shape configuration areorthogonal.
 2. The method of claim 1, wherein at least one of thephotosensitive substances is a bar made of one of an optical storagematerial and a photosensitive material.
 3. The method of claim 1,wherein at least one of the reflective layers is formed by coatingreflective material.
 4. The method of claim 1, wherein at least one ofthe reflective layers is formed through vapor deposition of reflectivematerial.
 5. The method of claim 1, wherein the photosensitivesubstances are arranged into an array.
 6. The method of claim 5, whereina combination of the photosensitive substances becomes at least onesheet structure after the cutting.
 7. The method of claim 6, furthercomprising: burnishing the sheet structure.